(1) Field of the Invention
Embodiments of the present invention relates generally to a microtome having an oscillating blade. More particularly, this invention relates to a microtome having flexure drive in the form of a pair of compliant mechanisms having substantially orthogonal axes of predominant stiffness, configured to oscillate a blade transversely to a direction in which the cut advances.
(2) Background Information
A microtome is a sectioning instrument that allows for the cutting of thin slices of material known as sections. Microtomes are an important device in microscopy preparation, allowing for the preparation of sections for observation under transmitted light in optical microscopy, or in block face imaging, a microtome may be used to successively remove portions of the sample to expose the sample interior for imaging of the remaining specimen block. To section a sample, a blade similar to a razor blade is used which is drawn across the sample thus removing a thin slice of the specimen under consideration. Microtomes generally use steel, glass, or diamond blades depending upon the specimen being sliced and the desired thickness of the sections being cut. Steel blades are typically used to prepare sections of animal or plant tissues for light microscopy histology.
Oscillating blade microtomes are a variation of the basic microtome, and are widely recognized as superior for cutting thick sections from non-embedded or fresh tissue samples. The vibration amplitude, the vibrating speed, the angle of the blade, and the feed rate (of tissue samples) may all be controlled allowing for optimization of the cutting process. Fixed or fresh tissue pieces are typically embedded in low gelling-temperature agarose. The resulting agarose block containing the tissue piece is then glued to a stand and sectioned while submerged in a water or buffer bath.
Examples of conventional oscillating microtomes are disclosed in U.S. Pat. No. 6,651,538, entitled Microtome (the '538 patent), and U.S. Pat. No. 6,041,686, entitled Microtome Having an Oscillating Blade (the '686 patent). In the '538 patent, blade oscillation is provided by attaching the blade to a movable body that is coupled to a base by a resilient coupler. The base is provided with a driving electromagnet, and the movable body is provided with a permanent magnet. The movable body is then oscillated by supplying a control signal to the driving electromagnet. The '686 patent discloses an articulated connection coupled to an eccentric that converts the circular motion of an electric motor into an oscillating, substantially linear motion. These approaches each suffer from disadvantages associated with relatively imprecise oscillatory motion, including parasitic error motions, which tend to result in imprecise section thicknesses and tissue damage.
The '686 patent and similar motorized configurations may offer improved cutting accuracy relative to the directly-driven solenoid approaches of the '538 patent and the like. However, such motorized approaches suffer from disadvantages due to backlash inherent in the joint of the articulated arm. A joint is not perfectly stiff, and the magnitude of the backlash may be on the order of tens of microns to several hundred microns, introducing both higher order harmonics into the motion of the blade, and parasitic motion along orthogonal axes.
Drawbacks are also associated with the alternate approach disclosed in the '686 patent, of using a guide rail to guide the motion of a leaf spring connected to the blade assembly. In this alternate approach, as well as the articulated arm approach discussed above, the guide rail disadvantageously limits the upper frequency and magnitude of the oscillations due to friction between the oscillating spring/arm and the stationary rail. Furthermore, again due to backlash or imperfections of the guide rail, it is difficult, if not impossible, to eliminate unwanted motions perpendicular to the blade motion.
Another issue is potential buckling of the leaf spring. Any buckling would tend to reduce the stiffness along the desired direction of motion. Moreover, the friction from the guide rail generally leads to instrument wear and required maintenance.
There is therefore a need for an improved microtome that addresses the drawbacks of the prior art.